Large scale heat sources are used for a variety of applications in industry, including sulfur recovery units, waste incinerators, and the like. Such heat sources typically have a construction as shown in FIG. 1, wherein a large-scale heating vessel 1 has a burner 2 on one end and a waste heat boiler 3 on the other end.
Waste heat boilers are commonly used with many types of industrial heat sources to extract heat from waste gases of an industrial process. It may be necessary to extract heat from the waste gas to cause a component thereof to condense, or it may be advantageous to extract heat from the waste gas and use that heat in another process or even to provide heat for the industrial facility.
Generally speaking, a waste heat boiler includes a plurality of metal boiler tubes 4 supported by opposed metal tube sheets 5 (only one tube sheet is depicted in FIG. 1). The tube sheets define a vessel for holding water or some other form of heat transfer medium. Hot waste gas passes through the boiler tubes arranged in the inlet tube sheet and heat is extracted therefrom via heat transfer from the hot gas to the heat transfer medium contained within the confines of the tube sheets.
There are several concerns associated with such industrial heat sources, e.g., incinerators. One concern is the corrosive nature of the heat and gas produced by the incinerator flame, and the damage that such heat and gas can inflict on the metal components of the waste heat boiler. In an effort to deal with this problem, the present inventors disclosed, in copending application Ser. No. 08/630,473, the entirety of which is hereby incorporated by reference, a new refractory ferrule to protect the metal components of the waste heat boiler from the corrosive nature of the incinerator heat/flame. A plurality of refractory ferrules are arranged to form protective wall 7.
Another concern is making use of the full heat exchange capability of the waste heat boiler. That is, the vessel 1 shown in FIG. 1 typically has a length of about 20-30 feet and a diameter of about 6-10 feet. The incinerator flame, however, is typically not as long or wide as the vessel. As a result, only the central tubes of the waste heat boiler receive the main thrust of the incinerator flame and a hot spot is created at the center of the tube sheet.
In an attempt to spread the heat of the incinerator flame across the entire face of the tube sheet of the waste heat boiler, it has become industry practice to erect a diffusor wall 6 between burner 2 and tube sheet 5 of waste heat boiler 3, as shown in FIG. 1, in an attempt to spread the incinerator flame over the full surface of tube sheet 5. Such diffusor walls have been formed of standard refractory brick, typically 9".times.4.5".times.4.5", in the shape of a standard wall, except that alternating bricks were omitted to give the appearance of a checkerboard (these walls are sometimes referred to as "checkerwalls"). The holes formed in the wall allow passage of the incinerator gas and provide more uniform heat distribution across the entire face of the tube sheet of the waste heat boiler.
This type of wall, however, has several drawbacks. First, the open frontal area of this type of diffusor wall is only about 35%, so that the presence of the wall substantially disrupts the volume flow of heated gas through the waste heat boiler.
Another drawback is that the bricks that make up the wall are mortared in place to withstand the force of the gas passing through the vessel. The service entrance of the vessel is near the burner, and thus the checkerwall, if not equipped with a "manway", must be dismantled each time the tube sheet of the waste heat boiler needs to be serviced or replaced.
Another type of checkerwall has been constructed from a plurality of refractory cylindrical tubes stacked one on top of the other like a pile of firewood. This structure provides greater open frontal area, but still must be dismantled when the tube sheet needs to be serviced. If the refractory tubes are assembled without the use of mortar in order to facilitate disassembly for tube sheet maintenance and repair, then the overall wall is highly unstable in the axial direction of the vessel, and the force of the gas emitted from the burner tends to displace the tubes in the direction of gas flow and collapse the wall.